This invention relates to measuring, and thereby making possible effectively controlling, the concentration of materials other than water used in a predominantly aqueous liquid composition for cooling and lubricating metal objects, particularly advantageously objects of tin plated steel and of aluminum and its alloys, while these objects are being severely cold worked. The invention is still more particularly advantageously applicable to conventional manufacturing of elongated cylindrical beverage containers, of the shape commonly used for millions of such containers per day in the United States alone, for beer, other carbonated beverages, and the like, from sheets of a suitable metal by two successive well established process steps. In the first of these steps, called “cupping”, a flat circular disk of the metal is formed into a relatively shallow “cup”. In the second of these steps, generally known in the art as “drawing and ironing” or “draw-ironing”, this cup is elongated into the final container shape (exclusive of the top, which is separately formed and attached to the rest of the container). This invention is particularly adapted to, and will be described below primarily in terms of, use in the drawing and ironing stage of making elongated cylindrical beverage containers with aluminum alloy walls. However, the invention is also applicable to any other metal forming operation using a similar lubricant composition.
In a drawing and ironing process, the wall of the original “cup” workpiece is substantially thinned as it is elongated. This process generates so much heat that the aluminum alloy units being processed must be kept in contact during substantially the entire process time with a liquid coolant. The mechanical apparatus used in a drawing and ironing process is usually called a “bodymaker”. As a result the liquid coolant used is usually called in the art and will be designated hereinafter as a “bodymaker coolant”. This coolant consists predominantly of water, which provides most of the cooling effect, but in all modem high speed container making plants the bodymaker coolant also includes a distinct portion, exclusive of its water content, in order to provide better lubricating properties than would be exhibited by water alone as a bodymaker coolant. This distinct portion is widely known in the art and is designated hereinafter as the “bodymaker coolant lubricant” or “bodymaker lubricant”, which terms are considered equivalent in this specification.
Most if not all of the constituents of the bodymaker lubricant, although necessary and useful in the drawing and ironing process, are deleterious to the adhesion of paints, printing inks and lacquers commonly used in subsequent finishing of the containers. These materials are therefore usually removed, or at least diminished in concentration per unit area of container surface, by various cleaning processes applied to the containers between the drawing and ironing process and final finishing with these final finishing materials. Therefore, in order to maintain adequate control and economy of the overall container manufacturing and finishing operation, including the drawing and ironing process itself, it is important to control the concentration of bodymaker lubricant in the bodymaker coolant with at least moderate precision.
A bodymaker lubricant normally includes several constituents, one of which is often a substance formed by chemical association between at least one boric acid molecule and at least one amine molecule. (This substance is variously called in the art a “salt” or a “complex”; either term is considered equivalent herein, and this type of substance is often abbreviated hereinafter as “BAC”, from “Boric acid-Amine Complex”.) Other common constituents of bodymaker lubricants include amine salts of fatty acids, alkoxylates of fatty acids, “extreme pressure additives” as generally known in art, and other corrosion inhibitors. A practically important constituent of bodymaker coolant (and therefore also of bodymaker lubricant by virtue of the definition of the latter as all of the non-aqueous parts of the former), which is not usually added deliberately but nevertheless is usually present after any substantial time of use, is suspended fine particles of the metal from which the containers are being fabricated. These and any other chemical substances that may be present in the bodymaker lubricant as used, but are not present in freshly prepared bodymaker coolant that includes bodymaker lubricant as specified for the drawing and ironing process, are distinguished from the non-aqueous chemical substances present in freshly prepared bodymaker coolant by calling the latter collectively “bodymaker-lubricant-as-prepared” below.
Some ingredients of the bodymaker-lubricant-as-prepared may be adsorbed to a greater degree than others on the surfaces of the containers during the drawing and ironing process, and/or may be concentrated to a greater degree than others in a thin layer of bodymaker coolant which is carried along on the container surfaces to the next stage of overall container manufacturing (a process characteristic often called “dragout”). Furthermore, in most practical operations, one or more vessels open to the atmosphere contain a substantial fraction of the total volume of bodymaker coolant in use, so that evaporation of the more volatile constituents of the bodymaker coolant almost inevitably occur, and foreign matter can drop into the vessels. In one plant, it was even found that floor cleaning chemicals became admixed with the bodymaker coolant as a result of common pipework that was not known about until investigated after a control problem with the bodymaker coolant arose! For all of these and other reasons, it can not be safely assumed that all materials in the bodymaker lubricant, whether added during makeup or during replenishment of the bodymaker lubricant in the bodymaker coolant, will maintain the relative proportions in which they were added in the bodymaker coolant as a whole during any long time interval after they were added. As a result, in order to guide the replenishment necessary to maintain the concentrations of all the constituents of the bodymaker lubricant within their desired control conecntration limits at all times during the drawing and ironing process, it is necessary to make frequent measurements of at least one, and sometimes more, characteristics of the bodymaker coolant that are correlated in a known manner with the concentration(s) of all of the constituents of the bodymaker-lubricant-as-prepared that are present in a used working bodymaker coolant and that need to be controlled in order to achieve a satisfactory degree of consistency in the results of the draw-ironing step of the total manufacturing process.
Consistently attaining the desired degree of precision of control of concentrations, in the bodymaker coolant as used, of the constituents of bodymaker-lubricant-as-prepared has proved difficult in the art so far. Quantitative analysis of some of the constituents of a typical bodymaker-lubricant-as-prepared is inherently difficult, is complicated by the presence of other constituents of the bodymaker-lubricant-as-prepared, or both.
Prior art methods have usually included a step of separating a sample believed to be representative of the bodymaker coolant as a whole into two liquid phases in a manner thought to be reproducible, followed by measurement of some characteristic of only one of the phases. In one widely used method, the refractive index of a water-rich phase is measured after various means are used to induce phase separation. This method, which inherently measures only a bulk property of the phase on which the measurement is made, has been demonstrated to be satisfactorily correlated with the concentration(s) of the critical ingredients of the bodymaker-lubricant-as-prepared in the bodymaker coolant as a whole, but only if all of the inputs to the bodymaker coolant can be very well controlled. In fact, however, impurities from earlier process steps carried in on the container units themselves and/or impurities introduced from any other source into the bodymaker coolant as a whole can, and in commercial practice often do, cause the measurements of refractive index not to correlate satisfactorily with the concentration(s) of the critical constituent(s) of the bodymaker-lubricants-as-prepared.
Accordingly, one object of this invention is to provide a more reliable method of measuring or otherwise controlling, under practical operating conditions in high speed container manufacturing plants, the concentration(s) of each of at least those constituent(s) of practical bodymaker-lubricants-as-prepared that need the most critical control in order to achieve reliable results. Other concurrent or alternative objects are to provide a method that is relatively low in cost, is simple enough to be performed readily by operators with relatively little training, and/or will provide results quickly. Still other concurrent and/or alternative objects will be apparent from the description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities used in the description of the invention to indicate amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, “parts of”, and ratio values are by weight; the term “polymer” includes “oligomer”, “copolymer”, “terpolymer”, and the like; the description of a group or class of materials as suitable or preferred for a giving purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not necessarily preclude unspecified chemical interactions among the constituents of a misture once mixed; specification of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole; any counterions thus implicity specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding conterions that act adversely to the objects of the invention; the work “mole” means “gram mole” and the word itself and all of its grammatical variations may by used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; and the terms “solution”, “soluble”, “homogeneous phase”, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferable at least 1000, hours during which the material is mechanically undisturbed.